BMI of 25-30 is considered overweight or preobese and BMI of more than 30 is obesity. A BMI of more than 40 is moribund obesity and may need surgical intervention to correct obesity or bring down to normal.

As BMI goes up more than 25, the number of diseases and morbidity increases. The suffering from disease increase with increasing BMI. The higher the BMI the greater is the risk of disease and suffering.
Keep you BMI below 25 to remain healthy.